The invention is based on a method for fastening thin plates (in particular metal sheets) overlying one another, as generically defined herein.
This generic fastening technique has manifold applications, because it can be done without additional auxiliary fastening elements such as rivets, screws and the like, yet without impairing the quality of the fastening. Such fastenings are capable of being subjected not only to considerable tensile forces but to shear forces as well, and always have, in addition to the positive interlock by force, a positive interlock because of shape at the fastening site between the plates; nevertheless, despite all the advantages, there is still one disadvantage, which is that a bump formed by the fastening element protrudes from the plate plane, so that this type of fastening technique cannot be used universally. Other elements can catch on these bumps, or the bumps may represent undesirable protrusions, for example on parts that are to be painted.
A known method of this generic type (U.S. Pat. No. 3,934,327) produces stamped cams, in which a deforming and stamping process is followed by a compressing process, wherein the plate piece closer to the plates is widened by compression and with its edges grips the plates from behind (clinching). So that the sheet-metal bump will protrude as little as possible from the plate plane, an indentation is impressed into the plates by additional pressing tools, and the stamped cam is then formed inside this indentation, so that the fastening parts of the cam protrude insignificantly beyond this indentation. The disadvantage in any case is that protrusions are now present on both sides of the plates to be fastened; thus the above-addressed problem is not overcome, but only shifted elsewhere.
In another known generic method and corresponding apparatus (German Published, Unexamined Patent Application No. DE-OS 35 32 900), only a limited volume, which is determined by the size of a blind opening in the forging die, is available for the fastening element to the extent that it protrudes from the plate plane. Although this method does attain a firm fastening with only little protrusion of the sheet-metal bump, with at least one smooth plate side, nevertheless the disadvantage of this nub on the fastening element remains.